If the host is already defined,
no attempt to find or load a definition is attempted,
and false is returned.
If the host is not already defined,
but a definition is successfully found and loaded,
true is returned.
Otherwise, an error is signaled.

Logical pathname definitions will be created not just by
implementors but also by programmers. As such,
it is important that the search strategy be documented.
For example, an implementation might define that the
definition of a host is to be found in a file called
"host.translations" in some specifically named directory.